From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical report on issues with the Peregrine clutch, specifically concerning slipping, torque, and casing distortion.
| Identifier | ExFiles\Box 179b\3\ img022 | |
| Date | 7th January 1933 | |
| ORIGINAL. Da.{Bernard Day - Chassis Design} From Hs{Lord Ernest Hives - Chair}/Aln. c. to BY.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Aln.1/MA.7.1.33. PEREGRINE CLUTCH. X4057. The clutch made up on Borg & Beck lines to N.Sch.3513 gave some trouble on the test-bed through slipping. As designed and assuming a co-efficient of friction of .175 for the fabric against the cast-iron clutch rings, the maximum torque which the clutch could transmit would be 1185 lbs.ins. The maximum engine torque on the other hand is 1280 lbs.ins, so that there is actually a slight deficit in the clutch capacity. The drawing gives 1160 lbs.ins. as the intended maximum. Measurements of the coefficient however give a figure of .21 at low loadings which it is reasonable to suppose hold good at the heavier loadings and with this value the torque transmissible would be 1422 lbs.ins, which gives a margin of 11% over the engine torque. A examination of the clutch showed that the casing, which is made of RR.50 alloy, had bulged at the centre to the extent of 0.1" this being a permanent set with springs removed. The effect would be to reduce the spring pressure by nearly 5% and at the same time to incline their axes by about 1.0°. These amounts however, do not seem sufficient to account for the slipping. It was found that the brinell of the casing was 58 to 59 whereas it should be from 67 to 76, the indication being that it has not been finally heat treated. The pressure required to restore the casing to its proper shape was 1300 lbs, applied at the centre which is some four times as much as the equivalent force the springs could exert to produce the distortion. There are however, both "work hardening" and time effects, the former raising the elastic limit (e.g. after distortion) and the latter allowing a "creep" under a force which would not distort the material in a short time. In any case it is found that after re-assembling and removing the springs again after about a fortnight the casing has again acquired a set of about .050". We doubt whether, even with final heat treatment, the cover would be sufficiently stiff to withstand the full spring load which occurs when the clutch is disengaged. | ||